Under certain circumstances a network may change the system information (SI) at specific radio frames, but in order to be effective, it must first notify associated wireless transmit/receive units (WTRUs) about this change with a paging message during a time period defined as a modification period (MP). At the end of this MP, when a new MP starts at an MP boundary, the Evolved Universal Mobile Telecommunications System (UMTS) Terrestrial Radio Access Network (E-UTRAN) broadcasts the new SI and the WTRUs need to acquire this new SI. The WTRUs must use the updated SI to operate properly. There is a relatively short time period (or window) during which WTRUs must acquire the new SI.
It is possible that a random access channel (RACH) procedure can collide with the new SI MP boundary (which may also be referred to as a validity boundary). As shown in FIG. 1, this situation may create problems if not handled appropriately. A RACH procedure may start prior to receiving a paging message that indicates a SI change, or after receiving a paging message indicating such a change, but the RACH procedure may also run over the MP boundary. FIG. 1 shows a case where the RACH procedure starts after the paging notification and runs beyond the new SI MP boundary.
Network configuration updates may trigger a SI change (such as cell barring, access class barring, or a change in RACH parameters) that are critical to the RACH procedure or to the underlying radio resource control (RRC) connection procedure. Minor updates to the SI which have no impact on the RACH procedure and may also trigger a SI change.
Acquiring the new SI can take a significant amount of time. In connected mode, completing the required SI messages such as master information block (MIB), SI block (SIB)-1, and SIB-2 may take approximately 170 ms to 330 ms. If the periodicity of SIB-2 is 160 ms and SIB-2 is acquired successfully in the first attempt, the acquisition of the required SI will typically be approximately 170 ms. Under other conditions, the acquisition time could be longer, e.g., 330 ms. Thus, acquiring the full set of SI messages would take even longer.
In Idle mode, SIB acquisition time could be the same or longer depending on the periodicity of the relevant SIBs, excluding the Earthquake and Tsunami Warning System (ETWS) SIB acquisition. Current standards indicate that a WTRU may apply the received SIBs immediately (i.e., the WTRU does not need to delay using a SIB until all SI messages have been received). So for RACH access, the relevant SIB in SIB acquisition in Idle mode is still SIB-2, and the WTRU spends approximately the same amount of SIB acquisition time as in Connected mode. Before the SIB acquisition is complete in Idle mode, the RACH procedure will not have the appropriate system parameters for operation.